Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers produce strong copper that retains ductility

31.10.2002


This form of copper, produced by Johns Hopkins engineers, is stronger than the normal type of copper, yet it remains ductile, meaning it can stretch without breaking.
Photo by Will Kirk


Ma, a professor of materials science and engineering, and doctoral student Yinmin Wang examine a sample of a new strong form of copper that their team created in a campus lab.
Photo by Will Kirk


Extreme cold and high heat help optimize the metal’s microstructure

Combining old-fashioned metal-working techniques with modern nanotechnology, engineers at The Johns Hopkins University have produced a form of pure copper metal that is six times stronger than normal, with no significant loss of ductility.

The achievement, reported in the Oct. 31 issue of the journal "Nature," is important because earlier attempts to strengthen a pure metal such as copper have almost always resulted in a material that is much less ductile, meaning it is more likely to fracture when it is stretched. Strength, on the other hand, refers to how much stress a metal can tolerate before its shape is permanently deformed.



"We were able to get the strength of the pure copper up to and beyond that of copper alloys without adding any other metals to it and without sacrificing ductility," said En Ma, a professor in the Department of Materials Science and Engineering and a co-author of the paper. Ma said that such strong and tough pure metals could have applications in microelectromechanical systems, for which suitable alloys may be more difficult to produce and may be more prone to corrosion, and in biomedical devices, in which a pure metal may be preferable to alloys that could expose the body to toxic metallic or non-metallic elements.

To make the pure copper stronger, the Johns Hopkins engineers had to employ extreme cold and mechanical manipulation, followed by a carefully designed heat treatment. "A real significance of this project was that we showed what traditional metallurgical processing can do in the new era of nanotechnology," said Yinmin Wang, a doctoral student and lead author of the paper. Ma is Wang’s faculty advisor.

The researchers started with a 1-inch cube of pure commercial copper and dipped it into liquid nitrogen for three to five minutes at a temperature of -196 degrees C (-321 degrees F). After removing it, the researchers rolled the copper flat, cooling the sample between rolling passes, to a final thickness of about 1 mm. This affected the metal’s microscopic crystals, each consisting of atoms arranged in a lattice pattern. The severe rolling deformation created a high density of dislocations, meaning atomic planes had been moved out of their proper position within the lattice. The cold temperatures kept these defects from quickly moving back into their original alignment.

Next, the copper was placed in an oven for three minutes to bake at 200 degrees C (392 degree F.) "As they heated up, the dislocations began to disappear in a process called ’re-crystalization,’" Wang explained. "New, ultra fine crystal grains formed that were almost dislocation-free. The higher the stored dislocations density after rolling, the finer the re-crystallized grains during heating. In our copper, these new grains were only a couple of hundred nanometers in size, several hundred times smaller than the original crystals, making the copper much stronger than it was in its original form."

This change in strength occurred because of the reduction in grain size to a level similar to that of nanocrystalline materials, which are defined as materials with grain sizes less than about 100 nanometers. (One nanometer is one millionth of a millimeter). When the grains are smaller, Ma explained, more grain boundaries exist to block the moving dislocations, and the metal’s strength is increased.

By carefully controlling the temperature and the timing when they heated the metal, however, the Johns Hopkins engineers allowed about 20-25 percent of the copper’s crystals to grow to a larger size in a process called "abnormal grain growth," meaning non-uniform grain growth. According to the researchers, this final mix of ultra fine grains and larger ones, described as a "bimodal distribution," is what gave the new copper its coexisting high strength and ductility. "By manipulating the grain size distribution starting from a nanometer-scaled grain structure, we reached an inhomogeneous microstructure that is stable during stretching," Ma said. "That reinstated the copper’s ability to stretch uniformly without fracture, a feature very important for the formability of the high-strength copper when processing it into different shapes in forming operations."

Next, the researchers plan to test their process with other pure metals as well as metal alloys, which are widely used in manufacturing, to see if it produces the same change in mechanical properties. "Materials with uniformly nanocrystalline grains can give you very high strength, but usually not enough ductility," Ma said. "They are also difficult to process, often involving compaction of tiny nanocrystalline powders. If you want a metal that is both strong and ductile, you may want to go the bulk processing route described in this Nature paper. Our work demonstrates that extraordinary properties can be derived from a nanostructured material by first creating and then tailoring the ultra fine grain structures."


Other co-authors of the "Nature" paper were Mingwei Chen, an associate research scientist, and Fenghua Zhou, a postdoctoral fellow, both affiliated with the Johns Hopkins Department of Mechanical Engineering. The National Science Foundation provided funding for the research.

Images available of the researchers, a sample of the strong copper and microscopic views of the metal; contact Phil Sneiderman

THE JOHNS HOPKINS UNIVERSITY
OFFICE OF NEWS AND INFORMATION
3003 N. Charles Street, Suite 100
Baltimore, Maryland 21218-3843
Phone: 410-516-7160; Fax 410-516-5251

Phil Sneiderman | EurekAlert!
Further information:
http://www.jhu.edu/~matsci/people/faculty/ma/ma.html
http://www.jhu.edu/~matsci
http://www.jhu.edu/news_info/news/home02/oct02/copper.html

More articles from Materials Sciences:

nachricht Combining the elements palladium and ruthenium for industry
22.09.2016 | National Institute for Materials Science

nachricht Defects at the spinterface disrupt transmission
21.09.2016 | Eberhard Karls Universität Tübingen

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

Im Focus: Complex hardmetal tools out of the 3D printer

For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.

Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...

Im Focus: Launch of New Industry Working Group for Process Control in Laser Material Processing

At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.

In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...

Im Focus: New laser joining technologies at ‘K 2016’ trade fair

Every three years, the plastics industry gathers at K, the international trade fair for plastics and rubber in Düsseldorf. The Fraunhofer Institute for Laser Technology ILT will also be attending again and presenting many innovative technologies, such as for joining plastics and metals using ultrashort pulse lasers. From October 19 to 26, you can find the Fraunhofer ILT at the joint Fraunhofer booth SC01 in Hall 7.

K is the world’s largest trade fair for the plastics and rubber industry. As in previous years, the organizers are expecting 3,000 exhibitors and more than...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Experts from industry and academia discuss the future mobile telecommunications standard 5G

23.09.2016 | Event News

ICPE in Graz for the seventh time

20.09.2016 | Event News

Using mathematical models to understand our brain

16.09.2016 | Event News

 
Latest News

Chains of nanogold – forged with atomic precision

23.09.2016 | Life Sciences

New leukemia treatment offers hope

23.09.2016 | Health and Medicine

Self-assembled nanostructures hit their target

23.09.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>